This invention relates to a system for introducing flowable additive to paint, varnish, woodstain or the like contained in a closed (preferably lidded) container. "Paint" includes traditional paints based on organic solvents and also paints based on aqueous solvents many of which are known as emulsion or latex paints. The additive may be any material which can be caused to flow well enough to enable it to be introduced into the container. The invention especially relates to a system for introducing a dose of (usually liquid or semi-solid) colourant to a base paint contained in a lidded paint can and which system is suitable for use in retail shops or stores which supply tradesmen. Such introduction of colourants into paint in shops or stores is often known as "in-store tinting". In-store tinting allows a much wider range of colours to be offered than would be possible if cans of each individual coloured paint had to be stocked. This is because the space which would be needed to stock a large number of coloured paints is much greater than the space needed to stock cans of base paint and an equivalent number of doses of colourant. Other additives which can be introduced to paint, varnish or woodstain using the system include fungicides, foaming agents, rheology modifiers, components (usually a catalyst or accelerator) of a multi-component paint or varnish or additives which modify the appearance of a paint such as flowable particulate solids such as solids which impart texture to a paint or metal flakes always provided such solids can be made to flow.
Hitherto in-store tinting has usually involved removing the lid from the can (or even punching a hole in the lid), introducing the correct dose or doses of colourant into the can, replacing the lid (or plugging the hole) and finally shaking the can in a mechanical shaker to disperse the colourant. Removal of the lid creates an opportunity for the paint, varnish or woodstain to be spilled or splashed and so this type of tinting technique is generally inconvenient and not very suitable for use by inexperienced people, especially members of the public in self-service shops. Punching a hole in the lid requires the skilled use of a sharp tool and so it is a technique which is quite unsuitable for use by inexperienced people. A further difficulty is that care is needed to ensure that the correct dose of additive is introduced into the container. This is especially so when the additive is a colourant because the eye is very sensitive to variations in shade caused by a failure to add all of the colourant. The amount of care needed can be reduced by supplying measured doses of additive in capsules but even then care is still needed to avoid spillage and splashing. Care is also needed to ensure that a capsule is properly emptied otherwise not all of a measured dose of for example colourant will be introduced into the paint and consequently unacceptable variations in shade may occur.